It has been found that, in submersible motor driven pumps of the type described, the annular space which is bounded by the cooling jacket and through which cooling medium flows is not always completely filled by the cooling medium, the result being a reduced cooling performance. Since the motor is disposed vertically in the submersible motor-driven pump, air easily accumulates in the top zone of the annular space. Furthermore, accumulations of particles of dirt may occur which cannot get out of the annular space.